A reaction product of polyvinyl alcohol (PVA) and an aldehyde such as formaldehyde has been found to be an effective water loss control agent to be used in oil fields. See, for example, "New Mud System Gets Field Trial" by J. Block in the Oil and Gas Journal, Jan. 11, 1982, pg. 79-82; U.K. patent application No. 2,074,636A where the reaction product is combined with a solid, particulate silicate or aluminosilicate material to form a fluid loss control system; and U.K. patent application No. 2,073,228A where the reaction product is combined with a hydroxy containing aluminum component. The reaction product has been made in batches in the laboratory by reacting polyvinyl alcohol with sub stoichiometric amounts of an aldehyde such as formaldehyde in a 16% sodium sulfate solution. The pH of the sodium sulfate is adjusted to about 2.3. The PVA is then slurried with this pH adjusted 16% sodium sulfate solution and then formaldehyde is added in the form of formalin which is a 37% aqueous solution stabilized with methanol. The mixture is heated to about 16.degree.- 21.degree. F. (60.degree.-70.degree. C.) for about 10-15 minutes. The reacted solid is filtered to remove excess solution. The resultant filter cake is then placed in a batch dryer where it is dried to its pre-requisite total volatile content which is approximately 3 wt. % (determined at 100.degree. C.). The solid particles are ground and screened to give the desired size fraction which is packaged. Using this batch reactor and the required batch dryer results in large clumps or agglomerates. These large particles have a "gummy" appearance and they stick together. As a result these large particles must be ground to obtain the smaller particle sizes preferred for packaging.
In addition to the deficiency that this is only a batch process, it also requires five unit operations involving a reactor, a centrifuge to separate the product from the reactor liquid, a dryer, a grinder to reduce the size of the particles produced and a sieve to insure obtaining the required on size particles for packaging.